The footage released on Jan. 30 by Tokyo Electric Power Co. (TEPCO) showing what could be melted fuel inside the No. 2 reactor at the disaster-stricken Fukushima No. 1 Nuclear Power Plant has highlighted the difficulty of salvaging the object, which is apparently stuck to footholds and other equipment at the facility.
TEPCO took the footage as part of its in-house probe into the No. 2 reactor and found that black and brown sediments — possible melted fuel — are stuck inside the reactor’s containment vessel over an extensive area.
“If what was captured in the footage was melted fuel, that would provide a major step forward toward trying our hand at unprecedented decommissioning work,” said Yoshiyuki Ishizaki, head of TEPCO’s Fukushima Revitalization Headquarters, during a press conference in the city of Fukushima on Jan. 30. “The finding may provide a major clue to future work to retrieve the object,” he added.
At the time of the March 2011 meltdowns at the plant, there were 548 nuclear fuel rods totaling some 164 metric tons inside the No. 2 reactor, but they apparently melted down after the loss of power sources for the core cooling system, with part of the melted fuel penetrating through the pressure vessel before cooling down at the bottom of the containment vessel. The temperature of the reactor core topped 2,000 degrees Celsius at the time of the accident, melting metals including nuclear fuel inside the reactor.
The melted fuel has since come in contact with underground water flowing from the mountain side, generating radioactively contaminated water every day. In order to dismantle the reactor, it is necessary to take out the melted fuel, but high radiation levels inside the reactor had hampered work to locate the melted debris.
On Jan. 30, apart from the footage, TEPCO also released 11 pictures taken inside the No. 2 reactor. The images show the sediments in question stuck to metal grate footholds and water is dripping from the ceiling. Further analysis of those images may provide information on the current status of the disaster and positional clues to decommissioning work.
The in-house probe, however, has only focused on the No. 2 reactor, and there is no prospect of similar probes into the No. 1 and No. 3 reactors starting anytime soon as they were severely damaged by hydrogen explosions following the 2011 meltdowns.
In April 2015, TEPCO introduced a remote-controlled robot into the No. 1 reactor by way of a through hole in its containment vessel, but the device failed to locate melted fuel inside due to high radiation levels. While the utility is planning to send a different type of robot into the No. 1 reactor this coming spring, it would be difficult to carry out a survey similar to that conducted at the No. 2 reactor, as radiation levels are high around the through hole in the No. 1 reactor’s containment vessel, from which a device could access to right below the No. 1 reactor.
The No. 3 reactor, meanwhile, holds roughly 6.5-meter-deep contaminated water inside its containment vessel, a far larger volume than that accumulated at the No. 1 and No. 2 reactors. TEPCO has thus been developing a robot that can wade through water.